It is known that, during the phases of approach to an airport (initial, intermediate and final approaches and landing), an air traffic controller sometimes asks the pilot of a first aircraft—the seeker aircraft—whether he can see a second aircraft—the sought aircraft—in his field of view. If so, he may then ask him to fly visually by following this sought aircraft without overtaking it. Thus, the seeker aircraft clings on as it were to the sought aircraft in such a way that the air traffic controller then need no longer concern himself with this seeker aircraft. By decreasing the workload of the air traffic controller, such a procedure, termed “visual separation”, makes it possible to increase the number of aircraft that the controller can handle simultaneously and consequently to increase the volume of air traffic. Similarly, in the en-route phase, an air traffic controller may ask the pilot of an aircraft to “visually cling” to another aircraft. The controller can thus form a group of several aircraft that he can then handle as a single entity.
This type of procedure nevertheless has a drawback relating to the seeker aircraft pilot's difficulty in locating the position of the sought aircraft in his field of view without any risk of error. Specifically, multiple causes may impede this pilot in locating this sought aircraft. He may be impeded by meteorological phenomena, such as dazzle by the sun, presence of clouds, etc. and also be confronted with a risk of confusion if several aircraft are present in his field of view, in particular if they are close together according to the pilot's viewing angle.
It will be noted that the American document U.S. Pat. No. 6,348,877 describes a system for aiding the visual spotting of a sought aircraft by the pilot of a seeker aircraft, this system displaying on the canopy of the latter aircraft a symbol in alignment with said sought aircraft. However, it is quite obvious that this system cannot remedy the meteorological phenomena and the risk of confusion which were mentioned above.
Moreover, it is known that, on modern civil transport airplanes, the pilot has a display, commonly called the ND (Navigation Display) display on which the neighboring traffic can be represented according to various possible modes, based on information computed by its TCAS (Traffic Collision Avoidance System) system, or transmitted by air traffic control or by the other airplanes. However, these various modes of display generally correspond to a “plan view” cartographic representation of said traffic, i.e. in a plane substantially orthogonal to the plane of the field of view of said pilot through the canopy. They therefore do not allow the pilot to ascertain directly, in a realistic manner, the position of an aircraft in his natural field of view. Consequently, this type of display does not directly solve the existing problem, that is to say consisting in showing the pilot the location of an aircraft in his field of view. When, exceptionally, as described in the document EP-0 405 430, said ND display is disposed in a similar manner to the canopy so as to avoid the drawbacks of a “plan view” cartographic representation, the whole of the neighboring air traffic is displayed on said display, so that the pilot of the seeker aircraft may be confronted with the risk of confusion alluded to hereinabove.